NOW FIXED! 2002 MGTF VVC gone mad after flat battery (central locking doesn't work and won't start)

1628 Views 62 Replies 9 Participants Last post by D4KGP, 2 d ago

SimonMGTF160

Discussion Starter · 27 d ago

Greetings, I'm hoping someone has had this issue before and can suggest a swift and easy fix.

I was away in April so the car sat unused. When I went to open it a few days ago the central locking didn't do anything, it seemed the battery had gone flat, so I took the battery out and charged it on my trickle charger. It never got to 14.7 volts on the charger (where it would switch from "charging" to "trickle" mode), but it reached 13.8v after almost 48 hours of charging so I thought "good enough" and took it to the car.

The second both battery terminals were connected the horn started blaring continuously. Pressing the "unlock" button on the fob (two-button type) did nothing, so I unplugged the horn to save my ear drums. The interior lights remain on whenever the battery is connected.

Then I couldn't open the driver's door, even using the spare fob, which is only a few months old and previously worked perfectly as did the main one. Pressing the unlock and lock buttons on both fobs did absolutely nothing. I was able to get the driver's door open by manually turning the key with excessive force (why does that even work?!).

Once inside, turning the ignition on resulted in the front radiator cooling fan coming on. The windscreen wipers also started going continuously, despite not being turned on by the stalk. Turning the key to "start" mode produced a whirring noise as if the starter motor was spinning but not engaging the flywheel. I also noticed the passenger electric window goes down when you press "up" and vice versa. The drivers electric window no longer functions at all.

I'm now deeply perplexed and disturbed (even more than usual). Maybe the car battery is kaput? It was down to just over 12 volts after my wranglings, which seems very low given it was at 13.8v off the charger 20 minutes before.

None of the fuses in the engine bay are blown. The ones under the dash are trickier to check but none are obviously blown.

Does anyone have any suggestions? I'm currently recharging the battery...

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Roverlike

· #2 · 27 d ago

You need to know then each time you disconnect car battery you need to make resync process with ALL your fobs to the alarm system. This means you need to press unlock button 4-5 times, not too quick but also no too slow. Each time you disconnect car battery ALL your fobs lost sync and cannot be used without a resync.

Your horn came on as soon as you connected car battery because your car was locked and alarm armed when you took your car battery forbrecharge. To silence the hirns you need to press 4-5 times unlock button on your fob, first to resync the fobs, then to silence the horn.

Windows, wipers, erc start working is most probably bad earth connection. At this moment I do not have diagrams at me but I would check earth connections around car battery to panel since that one was last disturbed while you were removing your car battery.

Chris T

· #3 · 27 d ago

Is the car locked (with the key) before reconnecting the battery and re-syncing the fob?

SimonMGTF160

Discussion Starter · #4 · 27 d ago

Thanks Roverlike, are you saying I need to reconnect the battery and then press the "unlock" button on each fob 4-5 times? I'll try this. I'll also check the earths near the battery.

Chris, the car was locked (albeit with the bonnet open) when the battery was first reconnected. I've left the driver's door unlocked subsequently and tried reconnecting the battery. I also tried reconnecting the battery with the "bonnet open" sensor pressed down to try to make the car think all the "doors" (i.e. actual doors as well as boot and bonnet) were shut to try to make it calm down, but it didn't seem to work.

I'm not sure I've reconnected the battery with the door locked by key, and "bonnet open" sensor pushed down though, so I might give that a try. However all the strange behaviour with the fan and wipers is still quite concerning!

Roverlike

· #5 · 27 d ago

SimonMGTF160 said:
Thanks Roverlike, are you saying I need to reconnect the battery and then press the "unlock" button on each fob 4-5 times? I'll try this. I'll also check the earths near the battery.

Press 4-5 times on one fob when battery reconnected. You will easily resunc another fob little bit later.

SimonMGTF160

Discussion Starter · #6 · 27 d ago

I tried the "unlock driver's door with key then press unlock 4-5 times" method after reconnecting the car battery, no joy. I also tried it but pressing the lock button. What's meant to happen at the end of this sequence?

I tried another method I found online whereby you remove the key fob battery and each button on the fob ten times, it didn't make any difference.

The central locking continues not to do anything, and the car still won't start. Weirdly the "boot open" light on the dashboard is on permanently, unless the boot is actually open! The radiator cooling fan and windscreen wipers continue to run when the ignition is on. The EML and oil pressure lights come on on the dashboard at ignition but nothing else does, the fuel gauge goes up and down randomly.

All these electrical gremlins make me think something is malfunctioning but I'm not sure how to go about dianosing what, let alone how to fix it! Argh. More suggestions appreciated

Julian Foulger

· #7 · 27 d ago

Did you initially reconnect the battery + to the - and the - to the +? Have to ask as it has been known with the result that a car's control units are damaged beyond repair.

SimonMGTF160

Discussion Starter · #8 · 27 d ago

I didn't, although I did brush the ratchet against the bodywork while tightening the positive terminal up on the battery, causing sparks. For some reason I thought it was the negative terminal. Is there a way to make a certain diagnosis on this?

I noticed the ABS fuse is blown, and when replaced, blows again immediately.

Roverlike

· #9 · 27 d ago

When you say ABS fuse is blowing, I assume that is number 20 under steering wheel? If so that fuse controls ABS module, but also it controls fuses 1, 13, 14 and 25. That means instrument pack, wiper motor, alarm/central locking ecu and SRS ECU.
You need to find out what is blowing fuse number 20. Check fuses 1, 13, 14 and 25 if any of them is blown.

SimonMGTF160

Discussion Starter · #10 · 27 d ago

Yes fuse no.20 under the steering wheel. I will check the other fuses you mentioned next time I'm at the car.

I thought I'd check the big fuse under the boot in the engine bay (70A), this melted around six months ago causing the car to stop charging and eventually grind to a halt. I found just now it has blown. I replaced it with a spare 100A fuse, reconnected the battery, and the 100A fuse blew immediately (photo below). It seems there must be a serious short circuit somewhere, but how do I go about finding it?

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Julian Foulger

· #11 · 27 d ago

I changed the battery on my wife's Audi A6 only last week and the change requires programming et al so alot more complex than the MGF. I also, for a second, rubbed the ratchet against the + terminal on the battery and the body - massive sparks resulted(like a sparkler). The Audi has many individual control units and the thought did strike me that it could have been an expensive mistake. Fortunately, no problems resulted.

In your shoes, I would systematically go through all the car's functions and ascertain if there are any commonalities - ECU, SRS, body control unit (red box behind the passenger fuse box).

Roverlike

· #12 · 27 d ago

At this point I would stop changing fuses since with each fuse change you might do further damage along the lines. I would say it is time to inspect all the fuses, see what is burnt, but without changing it write down the burnt fuses. Then I would look at electric diagrams to see what these fuses cover and take out multimeter inspecting all the lines to see where is that power wire touching ground and causing all this havoc.
This might be long process.

Julian Foulger

· #13 · 27 d ago

The fuse in the engine compartment. Should be an 80 amp fuse.....looks like a 100 amp fuse from the colour.

Roverlike

· #14 · 27 d ago

Julian Foulger said:
The fuse in the engine compartment. Should be an 80 amp fuse.....looks like a 100 amp fuse from the colour.

OP said he replaced it with 100A and that blown too.

Roverlike

· #15 · 27 d ago

Since 80A alternator fuse is blown it well may be that diode pack on the alternator is over and providing direct link to ground. I would also disconnect terminals from alternator and check them to see if there you have ground connection. However, that might not be the only one.

SimonMGTF160

Discussion Starter · #16 · 27 d ago

I've now checked all the car's fuses, the only ones that are blown are the 70/100A large fuse in the engine bay (as pictured previously) and the ABS fuse under the steering wheel. I can't see any obvious chafed wiring etc at the doors/ bonnet/ boot hinge areas. It would be strange for that kind of issue to arise all of a sudden when the car's been stationary in any case.

I agree that replacing the blown fuses again without further remedial work is unwise.

I'll start investigating the alternator diode pack and look for any other possible shorts. Alternator was replaced six months ago in the same incident as the 70A fuse blowing (garage didn't notice fuse had blown so diagnosed charging fault as failed alternator and replaced accordingly...). However maybe my ratchet slip has damaged the diodes which has led to all this fuse-blowing m'larky.

Roverlike

· #17 · 27 d ago

SimonMGTF160 said:
I've now checked all the car's fuses, the only ones that are blown are the 70/100A large fuse in the engine bay (as pictured previously) and the ABS fuse under the steering wheel. I can't see any obvious chafed wiring etc at the doors/ bonnet/ boot hinge areas. It would be strange for that kind of issue to arise all of a sudden when the car's been stationary in any case.

I agree that replacing the blown fuses again without further remedial work is unwise.

I'll start investigating the alternator diode pack and look for any other possible shorts. Alternator was replaced six months ago in the same incident as the 70A fuse blowing (garage didn't notice fuse had blown so diagnosed charging fault as failed alternator and replaced accordingly...). However maybe my ratchet slip has damaged the diodes which has led to all this fuse-blowing m'larky.

Might be since plus (+) battery terminal is through 80Amps fuse directly connected to alternator diode pack.. However, I would not disregard one other possibility - that you have short on line from fuse to alternator and that came to surface again, while alternator is perfectly fine now as it was six months ago.

On the other hand you have connection from alternator to instrument pack battery bulb, which is powered from fuse 1 and in the line with fuse 20. Also management relay module with fuel pump relay and starter relay is powered over fuse 14, which is also in line with fuse 20. So need to check these as well.

SimonMGTF160

Discussion Starter · #18 · 26 d ago

I've been having a look at the larger cables around the 70A fuse, starter motor and altenator - can't see any damage to anything.

I wanted to check the diode pack on the alternator but it's fiendishly inaccessible, I'd need four hands to hold the torch, multimeter and both leads. I'd hoped the little removable access panel (see photo below) would help but no joy, you've got to go in from underneath, and I can't manage it. Is there a way to test the diodes via the 70A fuse socket? I'm not too knowledgeable on the old electrics unfortunately.

I fear I may be reaching the limits of my expertise and need to call in an auto electrician.

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SimonMGTF160

Discussion Starter · #19 · 26 d ago

Can anyone recommend a mobile mechanic who would travel to east London?

deepfat

· #20 · 26 d ago

Hate to say horse and bolted but I was taught regardless of polarity, battery out Earth 1st Live 2nd, battery in Live 1st Earth 2nd to avoid shorts.

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